Measurement of the Υ(1S), Υ(2S), and Υ(3S) polarizations in pp collisions at √s = 7 TeV

Chatrchyan, S. and Khachatryan, V. and Sirunyan, A. M. and Tumasyan, A. and Adam, W. and Aguilo, E. and Bergauer, T. and Dragicevic, M. and Erö, J. and Fabjan, C. and Friedl, M. and Frühwirth, R. and Ghete, V. M. and Hammer, J. and Hörmann, N. and Hrubec, J. and Jeitler, M. and Kiesenhofer, W. and Knünz, V. and Krammer, M. and Krätschmer, I. and Liko, D. and Mikulec, I. and Pernicka, M. and Rahbaran, B. and Rohringer, C. and Rohringer, H. and Schöfbeck, R. and Strauss, J. and Taurok, A. and Bencze, György and Hajdu, Csaba and Hidas, Pál and Horváth, Dezső and Siklér, Ferenc and Veszprémi, Viktor and Vesztergombi, György and Béni, Noémi Tekla and Czellár, Sándor and Molnár, József and Pálinkás, József and Szillási, Zoltán and Karancsi, János and Raics, Péter and Trócsányi, Zoltán and Ujvári, Balázs and Veres, Gábor and Krajczár, Krisztián (2013) Measurement of the Υ(1S), Υ(2S), and Υ(3S) polarizations in pp collisions at √s = 7 TeV. PHYSICAL REVIEW LETTERS, 110 (8). ISSN 0031-9007

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Abstract

The polarizations of the Υ(1S), Υ(2S), and Υ(3S) mesons are measured in proton- proton collisions at √s = 7 TeV, using a data sample of Υ(nS) → μ+μ− decays col- lected by the CMS experiment, corresponding to an integrated luminosity of 4.9 fb−1. The dimuon decay angular distributions are analyzed in three different polarization frames. The polarization parameters λϑ, λϕ, and λϑϕ, as well as the frame-invariant quantity ˜λ, are presented as a function of the Υ(nS) transverse momentum between 10 and 50 GeV, in the rapidity ranges |y| < 0.6 and 0.6 < |y| < 1.2. No evidence of large transverse or longitudinal polarizations is seen in the explored kinematic region.

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